Traumatic brain injury (TBI) diagnosticians traditionally have relied on subjective evaluations of the degree of injury to the brain or wait for expensive, highly sophisticated instruments, like MRIs, to diagnose a patient for brain injury. In battlefield conditions access to MRIs on scene are not practical. Subjective evaluation leads to undiagnosed and untreated brain injury until the trauma has caused irreversible injury. Prompt objective diagnosis and rapid therapy to minimize the effects of the brain trauma are essential to reduce damaging side effects, reduce medical costs long term and to improve overall outcomes. The introduction of objective measurement tools will provide the clinician with the ability to quickly, reliably, and routinely determine and monitor the state of the patient's injury during the initial diagnosis and throughout the treatment and recovery process.
In addition to inflammatory, infectious or autoimmune insult of peripheral cranial nerve, nerve root or brain stem in addition to neoplastic involvement of peripheral cranial nerve, nerve root or brain stem is a significant healthcare problem worldwide. Crucial to proper treatment and prognosis is an accurate assessment of neurological function. Universally, TBI assessment is accomplished according to the Glasgow Coma Scale (GCS)1. However, this assessment is not entirely applicable to all situations and the ceiling effect associated with the GCS makes this neurologic rating scale less sensitive for monitoring milder cases of TBI2. This can lead to a delay in appropriate treatment during the critical 24 to 48 hours after a suspected TBI when secondary brain damage is most likely to occur. Examples of limitations with the GCS include intubated patients who cannot complete the verbal response category, patients with temporary paralysis, or patients who are unable to complete the motor response test, such as with those treated using the current practice of early sedation3,4. In addition, a patient's GCS rating can have significant variability from diagnostician to diagnostician owing to its largely subjective nature5, 6, 7. In a London study of emergency neurosurgical referrals, it was determined that only 51% of patients arrived with accurate GCS scores8. The inherent subjectivity of the GCS, coupled with the previously mentioned ceiling effect for mild TBI, can result in the premature discontinuation of treatment or discharge of patients still in need of monitoring or treatment. Ultimately a one-point variation in scoring can mean the difference in deciding to send a patient to a Level 1 trauma center or not, having a significant affect on the care the trauma patient receives. In response to some of these limitations, ways to improve classification of patients with TBI are being developed9. Improved TBI description will not only offer considerable value for clinical trials10,11 but will also influence clinical management and specific therapies12.
Based upon available evidence and medical understanding of the physiological factors involved, a method and system providing reproducible, objective measurements of visual system dysfunction can provide a reliable indication of Mild to Moderate levels of Traumatic Brain Injuries (MMTBI). Such data will prove useful not only in the initial diagnosis, but will have significant value for prognostic and rehabilitative purposes.
One aspect of the present invention provides a method to develop and demonstrate a field deployable instrument capable of obtaining reliable measurements of visual function that could be used in the early diagnosis of MMTBI patients.
Another aspect provides an apparatus to measure an ocular response that objectively measures visual function to detect MMTBI31. The system and method of the present invention provides one or more of the following advantages; ease of use, fast, non-invasive, and objective measurements from the initial classification of a patient's neurological state, through the early stage treatment, drug response/effect and into the rehabilitation process. The instrument's ease of use will allow for frequent monitoring of a patient's condition during longitudinal assessment thereby providing quick, reliable assessment for field and clinical environments alike.
A benefit of one embodiment of the system and method is application to the military personnel serving in today's overseas combat operation where the occurrence of MMTBI is a daily threat. The relationship between visual ocular response and specific neurological conditions has not previously been thoroughly investigated.
TBI occurs when a sudden trauma, such as a blow to the head or penetrating head injury disrupts the function of the brain. Although, numerous methods have been proposed to measure, and thus classify brain damage, the Glasgow Coma Scale (GCS) is most commonly used for initial assessment of severity of damage1. Patients with MMTBI may exhibit a range of visual system dysfunction, including binocular, oculomotor, accommodative, visual field loss, refractive error shift, and visual perceptual deficits14,15. Unfortunately, visual system assessment is often not performed during the acute stage of medical intervention; in fact, more often than not, incoming patients do not receive a thorough evaluation of their visual system at all. The reasons that visual assessments are not routinely performed include the lack of a standardized mechanism and protocol that will operate and be applicable under the largely varying situations present and the lack of an established, direct correlation with MMTBI. For example, TBI assessments are often made at different points in time and under greatly varying conditions, such as at the site of injury, during transportation to hospital, in the emergency room, or prior to admission.
Early detection of MMTBI is of particular importance to the Department of Defense. Average rates of brain injuries in deployed personnel are over twice as high as in the civilian population16,17. Inadequate diagnosis of MMTBI can have immediate consequence on operations and long-term impact on victims. Service members with no apparent symptoms after an assault or other physical injury can develop complications anywhere from 2 hours to 6 days after the initial injury18. Symptoms can include cognitive problems such as fatigue, irritability, anxiety, dizziness and visual disturbances, which can affect the ability to function, especially in a high-stress combat situation19,20,21,22,23,24. These individuals are at risk of being inadvertently returned to duty and presenting an adverse risk to themselves, their comrades and their missions.
The preferred diagnostic technique for head injuries in Combat Support Hospitals (CSH) is structural imaging using computerized tomography (CT). CT imaging provides more clinical information than can be obtained from physical examination of a patient. Unfortunately CT imaging may show as negative for mild to moderate trauma. Magnetic Resonance Imaging (MRI) is often the preferred diagnostic technique for other neurologic insults, or disease. With the addition of MRI, especially when integrated with single-photon emission computed tomography, measurements can more accurately show the physiological extent of a lesion, disease or other neurologic injury of the brain25. This outcome, which can be true even for MMTBI, assumes that a patient has been first, adequately identified as a potential MMTBI case, and second, enough time has passed that an identifiable lesion has formed. Even so, the physical size, operational complexity, and logistics of MRI preclude its use in every CSH. Thus, a new system and method for clinical and research use suitable for field use is required to bridge the gap between CT and MRI.
An objective technique for reliable and repeatable assessment of ocular response to access central and peripheral neurological function in potential MMTBI patients for example, would provide a complementary test of neurological function.